I got two great ones off of ebay ( they easily light up a very LARGE space or a good portion of a single floor) I think I spent 12 dollars for each, tnad they can either directly hook up to your cam or you may simply plug them into a power supply. I was able to use one to fully illuminate a old iron work home.
It really is a matter of using the most sensitive camera and the strongest possible IR light source. I would hate to give one answer for all situations. The options can vary from a single very high power IR flood light, to multiple somewhat smaller IR light sources spread out through the area.
I personally have a 140LED IR flood light which I purchased a number of years ago. I originally purchased it for an outdoor IR camera system to monitor a yard. But it works great for investigations also.
